Knife sharpener



FIG. 1 is a front perspective view of the knife sharpener of the present invention;

FIG. 2 is a top view of the knife sharpener of FIG. 1;

FIG. 3 is a rear view of the knife sharpener of FIG. 1; and,

FIG. 4 is a right side view of the knife sharpener of FIG. 1, the left side being a mirror image thereof. 

CLAIM The ornamental design for a knife sharpener, as shown and described. 